Radiographic diaphragm and method of making the same



M. J. ZUNICK Sept. 17, 1957 RADIOGRAPHIC' DIAPHRAGM AND METHOD OF' MAKING THE SAME! Filed Jan. 21, 1954 Y 1NVENT0R: LQHAEL J. ZUNICK ATTORNEY 2,806,958' Patented Sept. 17, 1.957

United States Patent Office RADIOGRAPHIC DIAPHRAGM AND NIE'I'HD OF MAKING THE SAB/IE Michael J. Zunick, Greenfield, Wis., assigner to General Electric Company, a corporation of New York Application .ianuary 21, 1954, Serial No. 405,412

Claims. (Cl. Z50-63) The present invention relates in general to roentgenology, and has more particular reference to radiography, that is to say, the art of making enetrating ray pictures upon ray sensitive material, the invention pertaining especially to an improved radiographic diaphragm or screen of the sort commonly designated as a Bucky diaphragm, the same being adapted for use in connection with the making of radiographic pictures to improve picture denition, the present invention including improved procedures for making the diaphragm and comprising an extension of the invention disclosed in a co-pending application for United States Letters Patent Serial No. 331,014 iiled September 18, 1953 on the invention of Michael l. Zunick in Radiographic Diaphragm and Method of Making the Same, now abandoned.

Penetrating ray pictures, as is well known, may be made by passing penetrating rays derived from a suitable ray source through the object to be pictured and upon a layer of ray sensitive material either in the form of sensitive lluorescent screen means or ray sensitive iilm adapted to receive a latent picture image, and thereafter to be chemically treated for the development of the image. Radiographic shadow pictures tend to be of blurred character due to the nature of the material being pictured, including tissue structure as well as sectional thickness; secondary radiation, that is to say, radiation emanating from other than the primary source of picturing rays, and including secondary radian'on generated in the material of the picture subject as the result of exposure thereof to rays from the primary ray source; and perhaps other causes. The value of ray pictures, of course, in the nal analysis, depends directly upon the clarity and exactness with which they present the true internal structure of the object being pictured. Accordingly, ever since the establishment of roentgenology as an art, scientists, electrical technicians and others have been constantly striving to improve the character of shadow pictures by bettering the definition or clarity thereof.

Radiographic diaphragms of the sort first proposed by Gustav Bucky and described in Letters Patent of the United States No. 1,164,987, are commonly employed in radiography for the purpose of obtaining penetrating ray pictures of superior definition and clarity, numerous improvements having been made in the form, construction and utilization of such diaphragms as taught, for example, in United States Letters Patent No. 1,208,474 of December l2, 1916, on the invention of Eugene W. Caldwell; No. 1,551,162 of August 25, 1925, on the invention of Maurice Loebell; No. 2,115,755 of May 3, 1938, on the invention of Julius B. Wantz and Arthur I. Kizaur; and 2,435,823 of February 10, 1948, on the invention of Glenn W. Files.

Such radiographic diaphragms commonly comprise alternate grid strips of lead or other ray opaque material and strips of wood or other ray transparent material, the strips being arranged to form a composite plate or diaphragm in which the strips extend transversely of the plate and are angulated so as to permit only rays emanating directly from a primary ray'source to pass through thediaphragm between the ray opaque strips thereof, while tending to absorb in the ray opaque grid strips and thus exclude from the ray sensitive picturing material indirect, secondary, reflected and incidental rays originating from other than the primary ray source.

Radiographic diaphragms of the sort heretofore provided are relatively `costly structures because of the diculty in arranging the exceedingly tine gauge strips of ray opaque material in closely spaced and accurately angulated relationship in the grid structure. Much effort has heretofore been expended in seeking ways of reducing the cost of making radiographie diaphragms while at the same time improving the precision of strip angulation and preserving the individual line gauge strip material in flat, unbuckled condition in the structure, as evidenced by the several Letters Patent of the United States herein mentioned.

An important object of the present invention is to simplify and appreciably reduce the cost of making radiographicv screensfof the character mentioned; a further object being to provide a screen of the character mentioned by pre-forming a panel of material substantially opaque to X-rays with perforations disposed in a desired or preferred pattern in the panel to thereby form a grid comprising adjacent and alternately arranged ray opaque and ray transparent portions; another important object being to focalize the perforations in the panel by inclining the side forming surfaces thereof toward a common focus disposed outwardly of the panel on one side thereo and preferably vertically opposite the central portions of the panel; a still further object being to apply any suitable screen or preferred ray pervious material in said openings in order to form the panel as a continuous plate.

Another important object is to provide a radiographic screen of the character mentioned embodying a panel of ray opaque material formed with a multiplicity of -perforations extending through and distributed uniformly throughout the area of the panel, said openings, if desired, being lled with ray transparent material, whereby the screen may pass penetrating rays through said perforations while blocking the passage of rays through the panel at the panel portions which extend intermediate the perforations; a further object being to form the panel with focalized perforations all inclined toward a common focus, whereby the ray opaque material of said screen may substantially prevent passage through said screen of penetrating rays emanating from any source other than one located precisely at said focus.

Another important object resides in producing a radiographic diaphragm at low cost by pre-forming a panel of ray opaque material with focalized openings therethrough; a further object being to form the panel of ray opaque vitreous material such as glass and to provide ray transmitting window openings therein by dierentially etching the panel material in accordance with a desired window pattern.

Another important object is to form a radiographic diaphragm by exposing to light, -through a light screen of predetermined character, a panel of photosensitive glass, which is also substantially resistant to the passage of X-rays therethrough, in order to impose a desired latent light exposure pattern in the panel, thereafter treating the panel, as by heating the same, to develop the pattern in the panel in the form of relat-ively soluble and insoluble panel portions, then exposing the panel to the yaction of a suitable solvent whereby to form perforations through the panel by dissolving the soluble panel portions.

The foregoing and numerous other important objects, advantages, and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection "an object 15 to be radiographically Y with the accompanying drawings, discloses preferred embodiments of the invention.

Referring to the drawings:

' vention;

Fig. 2 is a sectional view of the improved diaphragm;

Fig. 3 is an enlarged sectional view through a portion of the diaphragm;

Fig. 4 'is a sectional view taken substantially -along `the Yline 4--4 in Fig. 3',

Fig. f5 isa sectional view similar to Fig. 4 and showing a modified form of the device; and

Fig. '6 is a greatly enlarged view of a portion of the diaphragm.

`To illustrate the invention the drawings show, in Fig. 1, radiographic equipment comprising a suitable pene- 'trating ray source, such as an X-ray generating tube 11, having an anode 12 providing .a substantially point source of X-rays `forming a ray beam'l. The equipment shown in Fig. 1 includes a suitable table 14for the support of pictured, diaphragm 16 embodying the 'present invention, and a sheet or lm of light sensitive material V17' enclosed in .a suitable cas- /sette 18 and disposed behind the diaphragm 16 in position to receive a rayv picture of the object 15.

In producing radiographic pictures, the presence, within-theeld ofthe useful ray beam 13, of objects, such vas particles Vor bodies 19Y of material capable of being rexcited by the4 ray beam to form secondary ray sources, will, in the Aabsence of the diaphragm 16, cause fogging of the picture formed in the layer or lm 17. ASuch fogging or blurring of `the picture, of course, is the result of "the action of secondary rays emanating from the source or sources '19 and tends to impair the clarity and definition of -the -resulting picture. Use ofthe vscreen 16, 'which is adapted to withhold from the layer 17 `substantially all Vrays except those emanating in directions radially of the primary ray source 12, will eliminate picture blurring rays vfrom secondary ray sources, such 'as the sources 19. To this end, the screen or diaphragm 16 of the .present linvention comprises adjacent and alternately disposed screen portions, which respectively comprise V ray transparent 'and 'highly ray -absorptive material substantially-opaque to the passage of rays therethrough. 'The "ray `Vabsorptive screen portions Ymay Vbe disposed in the lscreen in accordance with any vsuitable or preferred pat- `tern, Vincluding the linear, laminate/dor1striated pattern of the sort #embodied Vin presently available diaphragms.

The ray absorbing diaphragm 'portions -of the 4present invention, however, preferably comprise panel portions of material that is resistant to the passage of X-raysftherethrough, such panel portions 'being deh-ned by and between-a multiplicity of perforations -formed in Vand through 'the panel, whereby X-rays originating from a source in alinement with the Iperforations -may pass readily-through the diaphragm at said perforations, the diaphragm preventing the passage ofX-rays through-the panel portions which extend between adjacent perforations, so-that-rays emanating from a source disposed other than in alinement with said opening will be blocked by said Vintervening panel portions and prevented from passing through the diaphragm. In diaphragms of the sort heretofore provided, the ray'opaque panel portions have invariably consisted of spaced apart grid strips of ray opaque ma- Vterial and intervening ray transparent spacing material arranged transversely of the diaphragm and in stacked vrelationship forming a at plate in lwhich ea-ch grid strip is relatively angulated with respect tothe yothers so that vthe several strips each lie in aplane passing substantially through a focus-at which an X- ray sourceywith which the screen is adapted to be used, may be located.

Among the diiculties heretofore encountered in building satisfactory radiographic diaphragms is that which arises from the necessity of maintaining the -grid strips accurately in relatively angulated position and in fiat planar condition in the diaphragm. Any deviation of a strip from the position which it is required to occupy for optimum radiographic results will introduce corresponding defects in pictures made as the result of ray exposure through the diaphragm. Grid strips in diaphragms of the sort heretofore provided have thickness of the order of 0.602 inch, and width of the .order of ylifu; inch, `the strips being spaced apart in the diaphragm a distance 0f the order of 0.015 inch, it being desirable to make the strips as wide as possible in one direction and as thin as possible in the other in the interests `of improved picture definition. Radiographic diaphragms lalso are currently made in square sizes having area `of vthe order of 30() square inches and up, in which the length of the transversely extending grid strips is of the order of 18 inches, such size being commonly considered to be the practical limit because of the diculty of maintaining longer and wider strips in accurately oriented and angulated position in the diaphragm structure, such diculties -being augmented by the exceedingly thin, foil-like character of the strip material.

In view of the foregoing Vdiiliculties, it'has heretofore been the practice to build up radiographic diaphragms by alternately ,laminating ray opaque metal foil with layers of ray transparent material, such as wood, cardboard and the like, to form a laminated stack,-then cutting laminated blocks of strip-like character from such stack, squeezing the blocks in order to differentially compress the somewhat resilient wooden spacing layers thereof to approximately angulate the ray opaque metal grid strips, and finally assembling la series of the strip-*like blocks and securing the same together to form ythe diaphragm. Such procedure is not only slow, time consuming, costly and laborious, but the grid strips, in the resulting screen, are only approximately disposed in the required optimum positions of relative angulation.

The present vinvention provides for the Yproduction of radiographic diaphragms of the character mentioned, in which the ray opaque screen portions are accurately positioned and angulated with a degree of'precision not'heretofore attainable, the ray absorbing portions of devices made in `accordance with the present invention being securely maintained in accurately-oriented position'in the screen 'as a characteristic of the inherent screen structure of the present invention. The present invention also provides for the fabrication of diaphragms comprising accurately angulatedray absorbing screen portions in fashion eliminating the laborious steps heretofore required in laminating, angulating, and assembling the 'several portions of the screen.

To these ends, the diaphragm 16vmay comprise a preferably .plate-like panel 20 'of'material which is substan- Vtially opaque, that is to say relatively resistant to passage therethrough of penetrating rays, such as X-rays, the panel being provided with a multiplicity of perforations 21 therethrough, said perforations, if desired, being eachllled with a suitable. vray transparent filling material 22. The present invention contemplates the fabrication of the panel 20 from photosensitive glass capable of being treated to form the relatively tiny perforations 21 therethrough with exact precision, in order that the finished screen may have optimum ray screening characteristics.

Photosensitive glass of the sort herein contemplated contains ingredients or glass components that are capable of forming photographic images in the otherwise clear glass when lthe `same is subjected rto the action of X-rays or ultraviolet radiation ,followed by heat treatment of predetermined character. The latent radiation impressed vphotographic image, when first developed byheat treatbeing confined to' t'heg'lass graphic image.

The so crystallized portions have different physical and optical properties from those of the surrounding glass material, such as differences in density, expansion coeliicie'nt, refractive index,and other properties, including solubility in dilute hydrofluoric acid. The differential solubility of exposed and unexposed portions of a panel of photosensitive glass makes it possible to form the panel 20 precisely with perforations having any desired size and shape and arranged in any desired pattern. A panel of photosensitive glass, accordingly, can be so formed with perforations of desired size and configuration by exposing the panel to radiation through an appropriate screen adapted to apply a desired photographic image of the perforations 21 in the panel, and by developing such image within the glass by heat treatment, and then treating the panel with a dilute solution of hydrouoric acid in order to etch out and thus remove the ray exposed panel portions. Suitable photosensitive glass for the purposes herein contemplated may comprise silica with substantial quantities of lead, barium or other ray screening component, modiiied by an alkali metal oxide, such as potassium oxide, and containing traces of copper, silver or gold as photosensitizing media. A suitable formula for the manufacture vof the glass may include the following components in quantities expressed in terms of proportional weight:

portions containing the photo- The foregoing formula is not at all critical. The silica component may be varied by perhaps as much as 50% of the amount stated. Either lead oxide or barium oxide -or both may be included in any desired proportion up to 4as much as 65%. The amounts of the lithium, potassium and Valuminum oxide components also may be substan- :tially varied, while the cerium oxide component may be omitted entirely although its inclusion appreciably improves glass photosensitivity.

The process of forming a .7l-dimensional photographic image within a piece of photosensitive glass, and then dissolving the image to provide a formed member having excised shape substantially exactly complementary to that of the photographic image, may be termed the chemical working of glass. The resulting product closely resembles that which might have been obtained by employing mechanical tools to drill, grind or otherwise remove the excised glass portions; but the product achieved by the chemical working of glass may be of infinitely more complex and fragile character than could possibly be attained by the mechanical working of the material. The iinished article produced by the chemical working of glass, however, may differ from an exact reproduction of the initially applied photographic image by an amount determined by the relative solubility of the exposed and unexposed glass regions.

In order to produce the radiographic diaphragm 16 of the present invention, a panel 20 of photosensitive glass may be exposed to ultraviolet light from a suitable source, as by contact printing through a suitable negative screen carrying therein the pattern of perforations 21 to be formed in the panel 20. The source of ultraviolet light employed for photographically exposing the panel 20 may comprise a small, intense mercury or carbon arc forming a substantially point source of ultraviolet light. During exposure the panel 20 may be spaced from the ultraviolet ray source a distance equal to the distance at which the finished radiographic screen is Ato be used .from the source o'f picturing X-rays; The 3-dimensional images of the perforations 21, accordingly, will be formed in the panel 20 radially of the exposing ray source, whereby the perforations 21 will all be inclined toward a focal point that is fixed with respect to the panel 20. The screen through which the panel 20 is exposed may comprise a drawing in ray opaque ink upon a ray transparent layer, the drawing comprising a projection of the required 3-dimensional pattern of the perforations 21.

After exposure the glass panel 20 remains transparent and colorless. The panel, however, may be exposed in a suitable oven to heat at a temperature between the annealing and softening'temperature of the glass for the length of time required to develop the photographic image in the glass. At temperatures of the order of 600 C. the time required for complete image development in the glass is of the order of one hour. After the image has thus been developed in the glass panel, the same may be allowed to cool slowly in order to anneal the glass. After development the exposed glass portions have a cloud white appearance, while the unexposed portions-of the panel remain transparent.

After development the panel 20 may be immersed in a preferably continuously stirred bath comprising an aqueous solution of hydroiiuoric acid at a temperature of the order of 20 C. The aqueous acid solution preferably has a concentration of the order of 5 such concentraiton alfording optimum differential solution rates with respect to the exposed and unexposed portions of the panel 20. Under such optimum conditions the solubility of the crystallized photographic image portions of the panel is of the order of fifty times that of the unexposed panel portions. ln terms of volume of material removed during immersion in the acid bath, the exposed glass dissolves approximately times faster than the unexposed glass portions. As a consequence, the perforations 21 may be formed in the panel 20 in exceedingly closely spaced relationship, whereby the X-ray opaque panel portions surrounding the perforations 21 and extending between adjacent perforations may be of desired exceedingly thin section, and the perforations themselves may be of relatively small sectional size.

ter the panel has been chemically worked to form the perforations 21 therethrough, the same, if desired, may be charged with any preferred filler material that is substantially transparent to X-rays; or the perforations may be allowed to remain empty. The perforations 21 may comprise slender channels of prismatic character, as shown in Figs. 4 and 5 of the drawings, or the same may comprise elongated slots; and, while it may be possible to form the perforations as cavities opening on one side of the panel 20 only, it is preferable to form the same as channels extending completely through and opening on the opposite faces of the panel. Where the channels 21 are of stem-like prismatic character, they may have any desired, preferred or convenient sectional shape including the circular and polygonal shapes shown in Figs. 4 and 5. After the formation of the channels 21 in the panel 20, the surface portions of the panel may be sealed to close the open ends of the channels 21. This may be accomplished in any convenient or preferred fashion, as by applying a ray transparent surface layer 23 of lacquer, heavy paper, cardboard, or metal to the face of the panel 20. Such surface covering layer may serve not only to retain whatever filler material may be disposed in the channels 21, but also to protect the opposite faces of the panel 20.

The radiographic diaphragm 16 of the present invention thus comprises a panel 20 of X-ray opaque material formed with channels 21 extending therethrough, said channels being uniformly distributed throughout the area of the panel and being inclined toward a common focal point spaced outwardly of and preferably in vertical alinement with the medial portions of the panel, whereby the diaphragm may ,function as a radiographic screen in conjunction .with a A:picturing ray source disposed at said :focal point. 4In that-.connection, it be seen that Vrays Vemanating .from the ray source will he permitted to :pass .throughathe screen at the openings or channels 21, but Vwill Vbe prevented Vfrom passing through the screen portions which surround the channels. Since the channels and -the ray opaque screen portions which separate the channels `are Vfocalized, only such-rays may pass through the screen as emanate from a ray source disposed at or closely `ad- ;jacent the focus 4.toward which `all of the channels are inc'lined. Rays emanating from sources disposed other -thansubstantially at said focus will necessarily impinge Vupon the ray opaque material surrounding the channels I.2;1;and.hencewil l be prevented from passing through the screen.

The panel 20 may be provided with a preferably metal edge frame 24 of channel shaped configuration applied .and secured to .the marginal edges of the panel 20, the said .marginal .edges being preferably encased in a channel shaped mounting strip 25 of resilient material, such Vas rubber, which ,may extend within the frame 24 and resiliently support the marginal edges of the panel 20 within .the frame.

The channels vZlimay, of course, be formed by action `of the'solvent Vacid applied simultaneously on opposite sides of the .panel 2G. Alternately, if desired, solvent action may be .coniined to one side of the panel by covering the other side with a protective coating, or by other- :wise .applying the solvent .to one side of the panel only, to thus dissolve Vthe glass portions to be removed in forming the channels 2l progressively from and inwardly of .one side of the panel.

In-orderto obtain adesired large over-all screen thickness, it maybe desirable to Vform the panel 29 as a lamienated structure, .by assembling and securing several separatelayers 26 in .stacked relation, with the faces of the `several layers in superficial contact at and along separa- :tion planes 27, eachlayer being formed with perforations Yin alinement with lcorresponding perforations formed in adjacent layers, whereby to provide perforations 21 of Ydesired configuration kand in a desired arrangement pattern in the laminated panel 20.

Vit is thought that the invention and its numerous at- `tendant advantages will be fully understood from the foregoin'g description, and it is obvious that numerous fchanges may be made in the form, construction and arrangement of `the several parts without departing from fthespiritor scope of the invention, orxsacricing any of its attendant advantages, the forms herein disclosed being preferred embodiments for the purpose of illustrating the c finvention.

The invention is 'hereby claimed as follows:

l. A radiographic .diaphragm comprising a plateof glass appreciably resistant to the passage of penetrating rays, such as X-rays,'said plate being formed with close- Yly spaced, axially straight, acid -etched ducts extending therethrough and disposed throughout the effective screen- 4ing area ofthe plate.

2. A radiographic diaphragm comprising a plate-of glass appreciably resistant to the passage of penetrating rays, such .as X-rays, said plate comprising photosensitive glassand being formed with closely spaced, axially straight, acid etched ducts extending'therethrough and Vdisposed through-out the effective screening area of the late. p 3. A radiographic diaphragm comprising a plate of glass appreciably resistant to the passage of penetrating `raysfsuch as X-rays, said plate being 'formed with close- `ly spaced, axially straight, acid etched ducts extending `therethrough and disposed throughout the effective screenfing area of :the plate, said ducts .being all mutually iniclinedinsaid'plate toward acommon focus disposed out- 'wardlyof-.the Vplateon one side thereof.

f4. .A-.radiographic :diaphragm comprising a plate Vof -glass appreciably jresistant to thepassage of penetrating rays, such as X-rays, said plate being formed 1with closely spaced, axially straight, acid etched ducts extending therethrough and. disposed throughout the effective screen- -ing area .of .the plate, said ducts being all .mutually inclined in said plate ,toward a common focus disposed outwardly of the kplate on one side thereof and in vertical .alinement with the medial portions vof said plate.

5. A .radiographic ydiaphragm comprising a plate of .glass appreciably vresistant to the passage `of penetrating rays, such as X,rays,said plate Abeing formed with closely spaced, axially straight, -acid etched ducts extending therethrough and disposed throughout the eiective screening area kof the plate, said ducts being of elongated prismatic .shape and being distributed ,thrcughout theV yscreening area of Athe plate v,in accordance with aselected duct distribution pattern.

6. A radiographic diaphragm comprising a plate ;of glass appreciably yresistant tothe passage of penetrating rays, such .as X- rays, said plate being formed with closely spaced, 'axially'straigha acid Vetched ducts extending therethrough and disposed ,throughout the eective screening area of the plate, said yducts Vhaving circular sectional configuration andbeing distributed throughout the screen- -ing area of the plate in accordance with a selected duct distribution pattern.

7. A radiographic diaphragm comprising a plate of glass appreciably resistant to the passage of penetrating rays, such as X-rays, said plate being formed with close- Yly spaced, axially straight, acid etched ducts extending therethrough and disposed throughout the effective screening area ofthe plate, said ducts having polygonal sectional configuration and being distributed throughout the screening area of the plate in accordance with a selected duct distribution pattern.

8. A radiographic diaphragm comprising a plate of phot-osensitive glass appreciably resistant to the passage of penetrating rays, such as X-rays, and conditioned for differential acid etching by exposure to light applied as a diierential intensity .exposure pattern, said plate having elongated, axially straight and closely spaced acid etched ducts formed in the plate substantially throughout its effective screening area, in accordance with Ya Vselected light exposure pattern.

'9, A radiographic diaphragm comprising a plate of Vphotosensitive Vglass appreciably resistant to the passage Y of penetrating rays, such as X-rays, and conditioned for differential acid etching by exposure -to light applied as a -dhierential intensity exposure pattern, said plate having elongated, axially rstraight and closely spaced acid etched `ducts formed in the plate substantially Vthroughout lits eiective screening area, in accordance with a selected -light exposure pattern, said ducts being all axially inclined toward a common focus outwardly of the plate on one side thereof.

l0. A radiographic diaphragm comprising a plate of -photosensitive glass Vappreciably resistant to the passage fof penetrating rays, such as X-rays, and conditioned for ,differential acid etching by exposure to light applied as a differential intensity exposure pattern, said plate having elongated, axially straight and closely spaced acid-etched ducts formed in the .plate substantially throughout its eiective screening area, in accordance with a selected light exposure pattern, the length of said ducts being more ythan -four times the maximum diameter thereof.

ll. A radiographic diaphragm comprising a plate of vphotosensitive glass appreciably resistant to the passage vof penetrating rays, such as X-rays, and conditioned for .diterential acid etching by exposure to light applied as a differential intensity exposure pattern, said plate having elongated, axiallystraight and closely spaced acid-etched ducts 'formed in the plate substantially through-out its eective 'screening area, in accordance with Va selected light exposure pattern,said ducts having -a ratio of Ylength to maximum diameter of the order of twelve.

.12.. -Airadiographic .dianhragm .comprising a plurality of laminations secured in stacked relation to form a panel having the faces of the several laminations inv superficial contact, said laminations comprising material appreciably resistant to the passage of penetrating rays, such as X-rays, and having elongated, closely spaced and axially straight acid etched ducts formed therethrough, the ducts in each lamination being in coaxial alinement With corresponding ducts formed in the other laminations to thereby provide a multiplicity of elongated, closely spaced channels extending in the several laminations rof the panel throughout its effective screening area.

13. A radiographic diaphragm comprising a plurality of laminations secured in stacked relation to form a panel having the faces of the several laminations in superlicial Contact, said laminations comprising material appreciably resistant to the passage -of penetrating rays, such as X-rays, and having elongated, closely spaced and axially straight acid etched ducts formed therethrough, the ducts in each lamination being in coaxial alinement with corresponding ducts formed in the other laminations to thereby provide a multiplicity of elongated, closely spaced channels extending in the several laminations of the panel throughout its eEective screening area, and ray transparent material disposed in said channels to iill the same and thereby prevent the accumulation therein of dirt or other foreign matter.

14. The method of making a radiographic diaphragm which consists in exposing a sheet of photosensitive glass, through a foraminous screen, to photographically exciting rays from a ray source of limited size disposed in position spaced from said sheet on one side thereof, whereby to apply the foraminous pattern of said screen as a latent 3-dimensiona1 photographic image comprising axially straight, rod-like portions of the sheet disposed Within and through said sheet and axially inclined toward said source, heating the exposed sheet to develop the said latent image therein and then etching the developed sheet with acid to dissolve said rod-like portions and thereby form axially straight ducts in said sheet in accordance with said image and inclined toward a common focus spaced outwardly of the sheet on one side thereof.

15. The method of making a radiographie diaphragm which consists in exposing a panel of photosensitive material to photographically exciting rays emanating from a ray source of restricted size and delivered through a foraminous screen adapted to guide the exciting rays to penetrate elongated, closely spaced rod-like portions of the panel in directions extending radially of the ray source, while screening from the action of said rays the portions of said panel which surround and separate said rod-like portions, thereafter heating the panel to render said rod-like ray exposed portionsvmore readily soluble than the screened portions, and thereafter dissolving the ray exposed portions of the panel by immersing the same in acid, whereby to form elongated, closely spaced and axially straight channels in the panel in position extending radially of a focal point outwardly of the panel on one side thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,381,521 -Tousey June 14, 1921 1,530,937 Gunther Mar. 24, 1925 2,353,145 Chamberlain July 11, 1944 2,566,265 Tuttle Aug. 28, 1951 2,628,160 Stookey Feb. 10, 1953 

